1. Field of the Invention
The present invention relates to a charged particle beam pattern forming apparatus and a charged particle beam pattern forming method and, for example, relates to a charged particle beam pattern forming apparatus and method capable of correcting misregistration originating in the amount of charge when a pattern is formed on a target object by using a variable-shaped electron beam.
2. Related Art
A lithography technique which leads development of micropatterning of a semiconductor device is a very important process for exclusively generating a pattern in semiconductor manufacturing processes. In recent years, with an increase in integration density of an LSI, a circuit line width required for semiconductor devices is getting smaller year by year. In order to form a desired circuit pattern on such semiconductor devices, a high-precision original pattern (also called a reticle or a mask) is necessary. In this case, an electron beam pattern forming technique essentially has an excellent resolution, and is used in production of high-precision original patterns.
FIG. 12 is a conceptual diagram for explaining an operation of a variable-shaped electron beam pattern forming apparatus. The variable-shaped electron beam (EB: Electron Beam) pattern forming apparatus operates as described below. In a first aperture plate 410, a quadrangular, for example, a rectangular opening 411 to shape an electron beam 330 is formed. In a second aperture plate 420, a variable-shaped opening 421 to shape the electron beam 330 having passed through the opening 411 of the first aperture plate 410 into a desired quadrangular shape is formed. The electron beam 330 irradiated from a charged particle source 430 and having passed through the opening 411 of the aperture plate 410 is deflected by a deflector and passes through a part of the variable-shaped opening 421 of the second aperture plate 420 before a target object 340 mounted on a stage continuously moving in a predetermined direction (for example, the X direction) is irradiated with the electron beam 330. That is, a quadrangular shape which can pass through both the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 is formed in a pattern forming region on the target object 340 mounted on the stage continuously moving in the X direction. The scheme for causing a beam to pass through both the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 to form an arbitrary shape is called a variable shaped beam (VSB) scheme.
When a target object such as a mask to which a resist film is applied is irradiated with an electron beam, an irradiation position and the vicinity thereof may be charged with an electron beam irradiated in the past. Misregistration originating in such a charging phenomenon has not been seen as a problem in a variable-shaped electron beam pattern forming apparatus, but with the development of micropatterning, as described above, misregistration originating in such a charging phenomenon is becoming an issue. Particularly with the introduction of double-patterning technique, more improved precision of the pattern position of a photomask is demanded.
As a method of correcting the misregistration of beam irradiation, a method of preventing a charge on a resist surface by forming a charge dissipation layer (CDL) on a resist layer has been known. However, the charge dissipation layer has basically acidic properties and so is not compatible with a chemically amplified resist. Moreover, it is necessary to install a new facility to form a charge dissipation layer, further increasing manufacturing costs of photomasks. Thus, it is desirable to make a charging effect correction (CEC) without using the charge dissipation layer.
Regarding the correction of misregistration originating in a charge, a pattern forming apparatus that calculates an amount of correction of a beam irradiation position based on electric field intensity and irradiates the beam irradiation position with a beam based on the amount of correction is proposed (see JP-A-2007-324175, for example). According to such an apparatus, it is assumed that the linear proportionality is established between the distribution of irradiation amount and the distribution of charge amount and the distribution of registration amount is calculated from the distribution of irradiation amount via a linear response function.
To correct misregistration of the irradiation position originating in such a charging phenomenon precisely, it is necessary to calculate a beam trajectory by considering beam incident angle dependency by a deflector. However, misregistration of the irradiation position originating in a charging phenomenon has been corrected under the assumption that an electron beam is incident vertically. Thus, it has been impossible to make a precise correction. Further, according to a pattern forming method in which the stage moves continuously, the deflection position is determined by a data processing operation for forming a pattern in the end and so is revealed only during pattern forming. Accordingly, it is difficult to determine the deflection position before forming a pattern. Therefore, the stage continuously moving method has a problem that it is difficult to make a position correction that takes beam incident angle dependency into consideration (deflection position dependency) offline in advance before forming a pattern.